1. Technical Field
The present invention relates to spindle motors equipped with dynamic-pressure bearings, and to disk drive devices in which such spindle motors are employed. The invention relates in particular to miniature, low-profile, high-rpm spindle motors, and to disk-drive devices that drive at high speed data-recording disks 2.5 inches and under in outside diameter.
2. Description of the Related Art
Dynamic-pressure bearings are employed as spindle-motor bearings in hard-disk and other data-recording disk-drive devices. The bearings exploit the fluid pressure of a lubricating fluid such as oil interposed in between the shaft and the sleeve, in order to support the two letting the one rotate against the other.
A conventional spindle motor employing dynamic-pressure bearings of this sort is illustrated in FIG. 1. The spindle motor diagrammed in FIG. 1 is configured with a thrust bearing section c in between the undersurface of the rotor a and the upper-end face of the sleeve b, for causing lift on the rotor a, and is also configured with radial bearing sections e, e, in between the outer circumferential surface of the shaft d, which is furnished unitarily with the rotor a, and the inner circumferential surface of the sleeve b, for centering the rotor a and preventing the rotor a from rotating at a tilt. In addition, the stator g is fitted to a base member f into which the sleeve b is fixed, and meanwhile a rotor magnet h is mounted on the rotor a so as be opposite the stator 9.
In a conventional spindle motor of this sort, when the spindle motor is rotating the rotor a is lifted by the thrust bearing c configured between the undersurface of the rotor a and the upper-end face of the sleeve b; yet by virtue of a ring member i manufactured of a ferromagnetic material being disposed in a location on the base member f that axially opposes the rotor magnet h, the lifting force due to the dynamic pressure in the thrust bearing section c and the magnetic attraction acting in between the rotor magnets hand the ring member i are brought into a balance that supports axial loads put on the rotor a. This means that a thrust plate that would be installed on the end portion of the shaft in order to configure, together with the sleeve and a counter plate, another thrust bearing section is not adopted in the spindle motor illustrated in FIG. 1.
Consequent advantages to the spindle motor depicted in FIG. 1 are that it is made simple and low-cost with no appreciable degradation in bearing stiffness, and that the motor can be made thinner in profile. Nevertheless, as far as disk drives in which a spindle motor of this kind is employed are concerned, owing to gains in the amount of data that can be stored on data-recording disks and owing to shortened seek times, even faster rpm has been demanded from a spindle motor for driving such data-recording disks.
In spindle motors illustrated in FIG. 1 noted above, an axially oriented taper-seal area k as a means of preventing oil retained in the thrust bearing c from leaking out to the bearing exterior has been formed in between the outer periphery of the sleeve band the inner peripheral surface of an annular projection j provided on the undersurface of the rotor a; and the oil has been sealed in the taper-seal area k by the internal pressure of the oil being balanced with atmospheric pressure to form meniscus.
Inasmuch as the gap formed within the taper-seal area k broadens heading in the direction parting from the bearing section, the capillary force varies according to the position where the meniscus forms. Consequently, in a situation in which the amount of oil retained in the bearing section has decreased, oil will be supplied to the bearing section from the taper-seal area k; conversely, in a situation in which the volume of oil retained in the bearing section has increased on account of temperature elevation or another cause, the increase in oil will be accommodated within the taper-seal area k.
With the taper-seal area k in the spindle motor depicted in FIG. 1 being disposed to the outer periphery of the radial bearing sections e, e, the taper-seal area k is not configured ranged in the axial direction beyond the bearing sections, which are the thrust bearing section c and the radial bearing sections e, e. This means that the spindle motor may be made still thinner while maintaining bearing stiffness.
Nevertheless, because the taper-seal area k is located radially beyond the bearing sections, during rotation the effect of centrifugal force on the oil retained in the taper-seal area k proves to be stronger by comparison to a situation in which the taper-seal area is configured for example axially adjoining the radial bearing sections. Since the oil within the taper-seal area k is consequently pressed under centrifugal force radially beyond the sealing area, the meniscus becomes misshapen, which impairs the sealing strength. The meniscus will therefore easily be destroyed and oil will leak if the motor undergoes vibration or shock. By the same token, if the spindle motor were to run at even higher rpm, increase in oil volume would be remarkable since the amount of heat produced in the motor would grow. What is more, oil that has undergone thermal expansion becomes less viscous, making the oil more susceptible to the effect of centrifugal force. Consequently, the amount of oil inflowing from over toward the bearing sections into the taper-seal area k interior increases. Given these circumstances, if owing to dimensional limitations in terms of making the spindle motor thinner in profile sufficient capacity cannot be secured for the taper-seal area k, restricted as it would be in axial dimension, oil inflowing into the sealing area would not all be accommodated, and thus oil would leak to the exterior of the bearing sections.
In hard-disk drives especially, when oil leaking from the bearing sections spatters within the drive device it sticks on the disk-recording surfaces and heads, becoming a causative factor giving rise to read/write errors. What is consequently needed in order to answer calls for accelerated rpm in, while maintaining a configuration that would enable slimming the profile of, spindle motors that are employed in disk drives is to make it possible to increase the capacity within the taper-seal area to retain a larger amount of oil, in a configuration in which the taper-seal area is arranged radially beyond the radial bearing sections, and moreover to render the configuration unlikely to leak oil from the taper-seal area interior.
An object of the present invention is to realize a miniature, low-profile spindle motor capable of rotating at high speeds.
A different object of the invention is to realize a spindle motor in which a large amount of oil can be retained and that also enables oil leaks and splashing to be prevented.
Another object is to realize a disk drive in which a large amount of data can be stored and yet in which miniaturization and profile slimming is possible.
Yet another object of the present invention is to realize a miniature, low-profile spindle motor superior in reliability.
In one example of a spindle motor by the present invention, radial bearing sections in which oil is the working fluid are formed in between the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, and a thrust bearing section is configured in between the upper-end face of the sleeve and the undersurface of a cap-shaped rotor. Formed in between the inner peripheral surface of the rotor cylindrical wall and the outer peripheral surface of the sleeve is a taper-seal area whose gap slopes from radially outward heading inward with respect to the rotational center axis and flares with further separation from the undersurface of the rotor. A boundary surface of the oil retained in the thrust bearing section forms within this taper-seal area.
Inasmuch as the taper-seal area is arranged radially beyond the radial bearing sections in the spindle motor described above, the taper-seal area is not ranged axially beyond the bearing sectionsxe2x80x94the thrust bearing section and the radial bearing sections. The axial span of the radial bearing sections will accordingly be large even though the spindle motor height is reduced, which thus makes increased xe2x80x9cconical stiffnessxe2x80x9d (stiffness against shaft wobble/run-out) in the radial bearing sections possible. What is more, by rendering the taper seal in a form sloping with respect to the rotational center axis, the tapered space functioning as the sealing area is lengthened, enlarging the capacity within the taper-seal area, and an oil boundary surface forms oriented in a direction sloping with respect to the rotational center axis. In particular, because this means that the boundary surface forms directed radially inward, during rotation centrifugal force will act in a direction pressing in on the oil boundary surface. Thus a structure in which the oil is unlikely to leak is rendered possible.
Since a spindle motor as described above for driving data-recording disks will furthermore have a large loading capacity and be highly stable, notwithstanding the spindle motor is miniature and slimmed, stabilized performance and advanced reliability can be had in disk drives for data-recording disks 2.5 inches and underxe2x80x94in particular miniature, slimmed disk drives that drive 1.8-inch and 1.0-inch data-recording disks.
From the following detailed description in conjunction with the accompanying drawings, the foregoing and other objects, features, aspects and advantages of the present invention will become readily apparent to those skilled in the art.